The present application claims priority from Japanese Patent Application No. 2001-301989 filed on Sep. 28, 2001, Japanese Patent Application No. 2001-304031 filed on Sep. 28, 2001 and Japanese Patent Application No. 2001-379711 filed on Dec. 13, 2001, all of which are incorporated herein by reference.
The present invention relates to a near-field spectrometer and, more particularly, to a background correction in near-field spectroscopy.
In recent years, the scanning near-field optical microscope has been developed based on the principle different from the principle for the common optical microscopes or electron microscopes. This microscope can observe the objects that are smaller than the wavelength of light, that has been difficult for the common microscopes and its applications are expected.
This scanning near-field optical microscope is to detect so-called near-field light. For example, when a minute sample is placed on a flat substrate, if a light is incident from the back of the substrate into the sample at an angle which gives rise to the total reflection, the propagated light is wholly reflected but a surface wave called near-field light is generated in the periphery of the surfaces of the substrate and the sample. This surface wave is present locally in the region that is around the sample and within the wavelength of the light.
Then, by inserting a probe having a sharp tip into the field of the near-field wave to scatter the near-field light and measuring the intensity of the scattered light, it is possible to define the distance between the tip of a probe and the surface to be measured of the sample can be grasped.
Therefore, by scanning with the probe keeping the intensity of the scattered light constant, the position of the tip of the probe reflects exactly the concavo-convex (topography) of the surface of the sample. In addition, the tip of the probe is present only in the field of the near-field light and does not contact with the sample itself. Thus, scanning near-field optical microscope is non-contact and non-destructive to the sample and can observe the objects that are smaller than the wavelength of the light.
Also in recent year, by attaching a spectral analyzer etc. to a scanning near-field optical microscope, even the components and the like of a sample can be analyzed as well as the topography information of the surface to be measured of the sample can be grasped. Therefore, a scanning near-field optical microscope is applied to the various fields. For example, the above analysis is performed by bringing the sample and the tip of the probe close to each other within the near-field region to collect the scattered near-field light and by spectrally analyzing the scattered light to obtain the spectral information.
However, even in the case of a near-field spectrometer that can obtain simultaneously the information on the height at each of portion to be measured on the sample and the information on its components, though further improvement of the items such as the precision of the spectral form, the efficiency of measurement has been desired, there has been no appropriate art that can cope with this problem.
The present invention was conceived in view of the above drawbacks in the prior art and its object is to provide a near-field spectrometer that can obtain efficiently the true spectral information on the sample.
To achieve the above object, the near-field spectrometer of the invention comprises a near-field information collector, a background information collector, a Z-axis scanner and a data processor.
The background information collector is characterized in that it separates in the Z-axis direction the sample and the tip of the probe from each other using the Z-axis scanner and obtain background information on the corresponding portion to be measured during the separation at a predetermined distance outside the near-field region.
The near-field information collector collects the scattered near-field light by bringing the sample and the tip of the probe close to each other within the near-field region, spectrally analyzes the scattered light collected and obtain the near-field spectral information on the sample.
The Z-axis scanner scans the sample and the tip of the probe in the Z-axis direction to separate them from each other and to bring them close to each other. When obtaining the near-field spectral information using the near-field information collector, the sample and the tip of the probe are brought close to each other at a predetermined distance within the near-field region. When obtaining the background spectral information using the background information collector, the sample and the tip of the probe are separated at a predetermined distance outside the near-field region.
The data processor subtracts the background spectral information obtained by the background information collector from the near-field spectral information obtained by the near-field information collector and obtains the true near-field spectral information after the background has been removed.
In addition, a plurality of surfaces to be measured are set on the sample surface to be measured as the portion to be measured for the near-field spectrometer of the invention. The near-field spectrometer of the invention further comprises an XY-axis scanner that scans the tip of the probe above the sample surface to be measured in the directions of the X-axis and the Y-axis that are perpendicular to the Z-axis.
Then, the near-field information collector scans the tip of the probe in the X-axis direction and the Y-axis direction of the surface to be measured using the XY-axis scanner under the situation that the sample and the tip of the probe are brought close to each other using the Z-axis scanner at a predetermined distance within the near-field region, and obtains the near-field spectral information on the surface to be measured.
The background information collector obtains the background spectral information for the surfaces to be measured that are a starting point and/or an arriving point of the tip of the probe during the separation of the sample and the tip of the probe from each other at a distance outside the near-field region by separating them in the Z-axis direction by the Z-axis scanner when the tip of the probe moves to the next surface to be measured.
It is preferable that the data processor subtracts the background spectral information on each of the surfaces to be measured from the near-field spectral information on corresponding surface to be measured and obtains the true near-field spectral information after the corresponding background has been removed, for each of the surface to be measured.
In the invention, a plurality of lines to be measured are set in a one-axis direction in the XY-axis surface on the sample surface to be measured as the portion to be measured.
The near-field spectrometer of the invention also comprises the XY-axis scanner that scans the tip of the probe above the sample surface to be measured in the X-axis and Y-axis direction that are perpendicular to the Z-axis. The near-field information collector obtains the near-field spectral information from each of the lines to be measured one by one.
The background information collector obtains the background spectral information for the lines to be measured that are a starting point and/or an arriving point of the tip of the probe during the separation of the sample and the tip of the probe from each other at a distance outside the near-field region by separating them in the Z-axis direction by the Z-axis scanner when the tip of the probe moves to the next line to be measured.
It is preferable that the data processor subtracts the background spectral information on each of the lines from the near-field spectral information on corresponding line to be measured and obtains the true near-field spectral information after each of corresponding background has been removed, for each of the line to be measured.
In the invention, a plurality of points to be measured are set on the sample surface to be measured as the portion to be measured. The near-field spectrometer of the invention also comprises the XY-axis scanner that scans the tip of the probe above the sample surface to be measured in the X-axis and Y-axis direction that are perpendicular to the Z-axis.
The near-field information collector obtains the near-field spectral information from each of the points to be measured one by one.
The background information collector obtains the background spectral information for the points to be measured that are a starting point and/or an arriving point of the tip of the probe during the separation of the sample and the tip of the probe from each other at a distance outside the near-field region by separating them in the Z-axis direction by the Z-axis scanner when the tip of the probe moves to the next point to be measured.
It is preferable that the data processor subtracts the background spectral information on each of the points from the near-field spectral information on corresponding point to be measured and obtains the true near-field spectral information after each of the corresponding background has been removed, for each of the point to be measured.
In the invention, the near-field spectrometer further comprises a light-distance characteristic collector and a selector. When the background spectral information is obtained using the background information collector, it is preferable that the separation distance in the Z-axis direction between the sample surface and the tip of the probe should be made by the Z-axis scanner the distance selected by the selector.
The light-distance characteristic collector obtains the relation between the light and the distance by obtaining the spectral information on the sample while the separation distance between the sample surface to be measured and the tip of the probe is being changed by the Z-axis scanner.
The selector selects the distance that gives the desired optical property, based on the relation between the light and the distance obtained by the light-distance characteristic collector.
The distance that gives the desired optical property, mentioned above, means the distance at which the background can be removed adequately without degrading the spectral waveform when obtaining the true near-field spectral information.
Further, in the invention, it is preferable that the Z-axis scanner is a moving device that scans the probe and/or a moving stage that mounts the sample and scans the sample.
Further, in the invention, it is preferable that the XY-axis scanner is a moving device that scans the probe and/or a moving stage that mounts the sample and scans the sample.
Further, in the invention, the near-field information collector comprises at least a light source, an optical fiber probe as the probe, a spectroscopy that spectrally analyzes the light scattered by the probe and a detector that obtains the near-field spectral information from the light spectrally analyzed by the spectroscopy.
Preferably, the background information collector comprises at least the light source, the optical fiber probe, the spectroscopy that spectrally analyzes the background light and the detector that obtains the background spectral information from the light spectrally analyzed by the spectroscopy.
It can use either system which uses dispersion element (dispersion type) or which uses interferometer (interferometer type) as the spectrometer in this invention.